Conventionally, hair cosmetics in the form of hair water have been known, in which an oily component is incorporated for the purpose of protection of the hair, improvement of the feel for touch, etc. Since this type of hair cosmetic is excellent in that hairs are softly manageable without stickiness and give light natural finish, many kinds thereof are proposed. However, if a large amount of an oily component is to be incorporated therein for further enhancing the performance, the cosmetic should be an emulsion form with a large amount of an emulsifier, causing problems such as deteriorating the feel for touch as compared to hair water, or difficulty of keeping the storage stability, so that the amount of an oily component capable of being incorporated is inevitably limited.
As means for solving the problems of both hair water type and emulsion type hair cosmetics, a two-layer separate type hair cosmetic has been proposed. This type of hair cosmetic consists of separated two layers and can be homogenized by shaking immediately before use, and is separated again after standing still for a while. This hair cosmetic provides a beautiful appearance, as well as an improvement of performances due to the capability of incorporating oily components in a large amount.
The two-layer separate type hair cosmetics are further classified into mainly the below two types:
1) Two-layer separate type, consisting of oil layer/aqueous layer (for example, Patent Documents 1 and 2), and
2) Two-layer separate type, consisting of emulsion layer/aqueous layer (for example, Patent Documents 3 and 4).
In the case of the oil layer/aqueous layer type of 1), when only an oil layer and an aqueous layer are simply used in combination, the two layers are mechanically dispersed, however immediately separated even by shaking immediately before use, and application thereof in a homogeneous form to the hair is thus difficult. By use of an emulsifier, it is possible to mix and emulsify homogeneously these layers while shaking, and to maintain the emulsified form, however in this case, a difficulty of the emulsion to be separated when being left standing arises (see [0004] in Patent Document 1). Thus, in the case of the oil layer/aqueous layer type, in view of the problem of obtaining a hair cosmetic which is “suitably emulsifiable and easily separable”, it is necessary to select a suitable emulsifier.
Meanwhile, in the case of the emulsion layer/aqueous layer type of 2), similar to the case of the above oil layer/aqueous layer type, a hair cosmetic must be shaken to mix the two layers homogeneously immediately before use, the homogeneous state must be maintained during application to the hair, and the two layers must be separated again after a while. However, since the upper layer has to be restored as an emulsion layer, optimization of temporal stability of the emulsion layer (see [0020] of Patent Document 3), as well as of the duration required for separation is necessary (see [0008] to [0009] of the same document). Moreover, in the processes of emulsification and separation of the oil layer/aqueous layer type, the “emulsion particles”, which are temporarily formed by shaking, gradually combine to form a large mass as time passes, and finally completely separated two layers are formed. In contrast, in the case of the emulsion layer/aqueous layer type, the “emulsion particles” are always present in the same condition and in the same particle size when homogeneously dispersed and when separated, and the “emulsion particles” (oily substance), having lower specific gravity than that of water, are gradually floated up and “volume of the lower layer (aqueous layer)” is changed, resulting to the separation of layers (see [0025] of Patent Document 4). Thus, the separation mechanisms of these two types are clearly different.
Furthermore, in the case of the emulsion layer/aqueous layer type, there is a unique problem where the aqueous layer sometimes becomes cloudy according to conditions even after the separation into two layers, which looks as if non-separated despite that they are separated, and thus, beautiful appearance cannot be obtained.
While, an emulsion layer/aqueous layer type cosmetic wherein a water-soluble polymer is incorporated for agglomeration of the particles in the clouding layer and for stabilizing them for a long duration has been reported (see Claim 1 and [0011] of Patent Document 5). The water-soluble polymer includes anionic and nonionic polymers, an anionic polymer is preferable, however specific compounds of the cationic polymer are not disclosed (see [0012] and Claim 3). Also, this cosmetic is intended to be used as a skin cosmetic, and there is no reference for using as a hair cosmetic.
Thus, there is no report for the two-layer separated type hair cosmetics (emulsion layer/aqueous layer type) satisfying the basic performances of hair cosmetics, such as temporal stability of the emulsion layer, appropriate separation rate (ordinarily, not greater than 24 hours, in view that a hair cosmetic is used at least once a day), beautiful appearance, and protection of hair and improvement of feel for touch.